Reduction of zinciferous material



Dec. 4, 1934. P. M., GINDER |..r AL

REDUCTION OE ZINCIFEROUS MATERIAL 4 2 Sheets-Sheet 1 Filed Dec. 30, 1931 (onde/75er 2 Sheets-Sheet 2 P. M. GINDER El AL REDUCTION OF ZINCIFEROUS MATERIAL Filed Dec. 50I 1931 /je'of Dec. 4, 1934.

h/a/er Patented Dec. 4, 1934 VUNIL'TED., STATES PATENT oF REDUCTION F ZINCIFERUS MATERIAL rhiup M. einser and Erwin c. Handwerk, ra1- merton, Pa., assignors to The New Jersey Zinc Company, a corporation of New JerseyI Application December 30, 1931, Serial No. 583,921

rica

BClaims.

some zinc in the form of metallic zinc (as vapor,

` liquid or 'solidi' orV zinc oxide is lost out of the bottom of .the retort. Furthermorait has been found that accretions of zinc oxide tend to build upon the cooler portions of the retort walls i near the bottom thereof, aswell as on the resiv due discharge mechanism, and such accx'etions --must be periodically removed.

We have discovered that this loss of zinc through the bottom of the retort is due primarily to theffact that while most of the zinc vapor produced in the heated portion of the retort passes to the condenser, some zinc vapor tends to diifuse downwardly to'ward the lower end of the retort which must in practice be kept relatively cool, for reasons hereinafter explained. That `portion of the zinc vapor that diffuses downwardlyimay condense as liquid or solid zinc Ion the walls of the unheated lower end of the retort, or on the residue discharge mechanism or yon the cooling residue itself. `If oxidizing conditions areencountered, zinc oxide will be formed and may be deposited as rock oxide accretions on the retort walls, the discharge mechanism or the residue. The accretions of rock oxide and solid metallic zinc must be periodically removed at considerable expense, and the deposits on the residue are lost in the discharge. If thebottom of the retort is maintained at such a high temperature that no condensation of zinc vapor occurs, there will nevertheless be some loss of i: zinc as vapor, especially when the residue is removed or withdrawn from the bottom of the retort. At a temperature of Boo-900 C. no condensation of zinc vapor occurs but rock oxide l 5 0 may form and be deposited on both the retort walls and the residue. l

Air entering at or near the bottom of the retort will intensify the formation of rock oxide. But even if air is excluded by sealing the bot- `5.5 tom of the retort, rock oxide may be produced (Cl. l5-28) by oxidation of metallic zinc vapor by carbon dioxide, the presence of which in the coolerportions of the zinc retort is an inevitable result of the chemical reactions that occur in thereduction of zinc oxide by carbonaceous material. The carbon dioxide is formed in two ways, viz:

(l) By the reduction of zinc oxide by carbon monoxide in accordance with the following equation:

ZnOzCO=Zn+COa 05 Not all of the carbon dioxide thus formed is reduced to carbon monoxide by reaction with the carbonaceous material of the charge, so that 4varying proportions of the carbon dioxide enter the relatively cooler parts of the retort, where temperatures prevail at which the reversal of the foregoing reaction takes place according to lthe following equation:

(2) At temperatures below 900' C., carbon monoxide tends to dissociate into carbon dioxide and carbon:

2CO==CQ1+C 80 'I'he carbon dioxide thus formed is available for oxidizing zinc vapor at the temperatures below 900 C. prevailing in the lower -cooler portions Since the oxidation of metallic zinc vapor in.\ accordance with either of the two foregoing reactions is notdue vto air or free oxygen, it is not possible to prevent the occurrence of either reaction by excluding air from the retort. 1 90 It is impracticable to prevent the oxidation of the metallic zinc -vapor bymaintaining the discharge end of a vertical zinc retort at such a high temperature (around 900 C.) that the carbon'dioxide present will not oxidize the zinc vapor, 95 because of the extra heat thus required and the diiliculty of handling such an extremely hot residue and operating the discharge mechanism at this temperature. In view of these difllculties, it is desirable from an operating standpoint to extend the retort downwardly some distance below the heated zone or portion thereof. so that the residue is cooled substantially below 900 C. prior to its discharge from the retort. Under certain conditions, it is advantageous to provide the lower extension of the retort with cooling means, such, for example, as water-cooling.

The present invention is concerned with decreasing tlie loss of zinc from the bottom of such zinc smelting retorts and'avoidlng the diiiiculties 1,10

incident to the deposit of rockoxide accretions. Thus, the invention contemplates an improved method ofV conducting the reducing operation so v as to substantially prevent zinc vapor from moving or diffusing downwardly from the active re* duction zone to the lower and cooler zone of the vreducing chamber Aor retort: E Theinvention accomplishes l this 'condition of operation by` the `introduction at or near the bottom of the reduc-g ing chamber of suiiicient gas to cause an upward g'as current of adequate volume and'velocityto.-`

- ducing chamber-having a` gaseous products outlet at a higher-level and a residue discharge at a lower level than the activel reducing mneof the cation of .the invention to a continuously operated vertical zinc retort (externally heated) will -be particularly considered for the purposes of explanation ahdvexampl'e, but it is to be understood that the principles of the invention are equally applicable to other Ityp'es of zinc reducing chambers.-

In carrying out the invention in conjunction witha continuously operated vertical zinc retort,

- it is now our preferred practice to close or seal 'thebottom of the retort, as for example, by a water seal, and to equip'the lower end of the retort with an appropriate residue discharging device such, for example, as a roller discharge.'

e 'I'he gas introduced at or near the bottom of the 'the following reactions:

'CO2+C=2CO oi`+2c=2co Excessive dilution of the retort ases by the carbon monoxide and hydrogen thus formed from the steam produced by the descent of the hot residue into the water seal may be prevented by water-cooling the lower portion of the retort or its downward extension if any, so as to lower the temperature of the discharged residue and thus decrease the amount of steam formed.

v The gas maybe blown under pressure or otherwise appropriately injected into the retort at or near its lower end and below the heated reducing zone of the retort. The introduction of the gas i should be so effected as to minimize the production of eddy currents within the charge in the retort. The primary aim in introducing the gas is to produce a positive, continuous and preferably uniform ii'ow of gas upwardly through theretort (and particularLv that portion of the retort below the cated reducing zone thereof) of such volume .d intensity as to substantially inhibit any counterflow of zinc vapor.

The amount of gas injected into the retort should be adequateto substantially counteract oxidizing constituents insuch large amount asl todevelop', through their reaction with carbon in the residue, enough heat tofuse or scorify any part of the rsidue'or the retort. In the actual 'practice off-the invention in the smelting of an agglomerated charge of mixed zinciferous and carbonaceous"materials in a vertical retort, one

foot by'lix feet in cross section and heated over a length or height of twenty-five f eet and producing about 7,500 pounds of metallic zinc perl day. two to four cubic feet of exhaust combustion Gases per/minute 'were introduced linto the bot- -tom vof the retort` with satisfactory results. The f exhaust gas from the externallyheated zinc rechamber. Inthe followingvdescription, the appli-V torl lsxictting, exit'gasfrom" the zincoondensers,

cer gas,air and steamv have been successfully employedin'carrying out the method of the invenuonm'-Y" Y' The invention may beconsidred in vconjunction with' the annexed drawings, which illustrate an embodiment of an apparatus for practicing the method ofthe invention.

Fig. i'is a side elevation partly in section of e a 'vertical' retort andits auxiliaries for producing zinc, equipped with means for practicingl the process of the presentinvention;

Fig. 2y`is an end-elevation partly in section of the apparatus shown in Fig. l; and

Fig. 3 is a cross-sectionon the line 3 3 of A vertical zincretot 10is so constructed that it can'be 'operatedgcontinuously -The retort is charged eitherl continuously or intermittently at the top with-agaspermeable charge, and the `residue is discharged atthebottom, as described in greateidetailV hereinafter'. 'I'he zinc vapor evolved 'from the retort is discharged through the oriiice'atthe top'of the retort, and may be .conducted to a condenser, as 'shown 'diagrammatically in'the t The retort heated by the combustion chamber 11 l(shown diagrammatically in Figs. land 2), equipped in conventional manner with fuel gas and air' inlets, and an exhaust gas main for withdrawing the* gaseous products of combustion;"' Y y The retort is providedkvvvithv a lower extension 12, extending below the combustion chamber and dipping into a water seal 13, into which thespent residue from the'reto'rt is'bdischarged. The extension is shownas equipped with a roller discharge 14,' situated a short distance above the waterseal. The said roller discharge maybe operated continuously or in rmittently, by a manual or mechanical drive o conventional type (not shown) ',The'extension may be constructed of metal and `may be water-cooled, in a conven- 12) according tothe hereinabove described proe- 150 Power for the injection 'of this gas is supplied by a fan 1'1, which forces the gas through a pipe 18 into the manifold 16 (see Fig. 3).

In Fig. 1, the fan 17 is shown as connected `by a valved bleeder pipe 20 with an exhaust gas main 21 leading away the exhaust gases from the' combustion chamber 11 that heats the vertical retorttl, so that exhaust gases from this source can be injected into the vertical retort through the inlets 15. The bleeder pipe 201s connected with valved branch pipes 22 and 23, through which air, producer gas -or other gases can be v likewise supplied to the fan 17 for injection into the vertical retort. `Inthis case the supply of exhaust gas from the exhaust gas main can be regulated or shut off by the valve in the bleeder pipe.

We claim:

, 1. In the reduction of an agglomerated charge of mixed zinciferous material and carbonaceous reducing agent in a vertically disposed externally heated reduction retort, the steps which comprise, sealing the spent residue discharge end of the retort against ingress of outside air and egress of inside retort gases and zinc vapor, introducing under pressure a controlled amount of exhaust gases from the combustion chamber surrounding 'the retort into the retort at or near its lower end to inhibit the flow downward in the retort of zinc vapor.

2. In the reduction of an agglomerated charge =of mixed zinciferous material and carbonaceous reducing agent in a vertically disposed externally heated reduction retort, the steps which comprise sealing the residue discharge end of the retort against ingress of outside air and egress of inside retort gases and zinc vapor, introducing under -prssure an appropriate gas at or near the bottom of the retort to provide a positive and substantially uniform upward ow of gas throughout that Y Iportion of the retort directly below` the active reducing zone thereof, said gas being selected from the group comprising exhaust gas from the ex- -jternally heated retort, setting, exit gas from the.

zinc in the discharged residue which comprises` introducing under pressure at or near the bottom ofthe retort gas of such a nature as not to produce sufcient heat in the retort to scorify the charge and in such quantities as to provide an upward flow of gas of sumcient velocity to prevent the downward diffusion of zinc vapor into the residue while not diluting the retort gases to such an extent as to interfere with the condensation of the zinc vapor. Y

4. 'I'he improvement in the reduction of zinciferous material in an elongated reducing chamber having a gaseous products outlet at a higher level and a residue discharge at a lower level than the active reducing zone of the chamber which comprises water sealing the spent residue discharge against ingress of outside air, and substantially inhibiting a downward flow in the chamber `of zinciferous vapors by introducing under pressure a controlled amount of an appropriate gas into the chamber at a level lower than the active reducing zone thereof, said gas being introduced into the reducing chamber at a plurality of spaced points to minimize the production of eddy currents within the charge inthe chamber and thus provide a positive and substantially uniform flow of gas throughout that portion of the chamber directly below the active reducing zone thereof.

5. The improvement in the reduction of a porous charge of mixed zinciferousand carbonaceous materials in a vertically disposed reducing chamber which comprises conducting the reducing operation with the residue discharge of the retort sealed, and inhibiting theow downward in the retort of zinciferous vapors by introducing under pressure a controlled amount of an appropriate gas into the retort at or near its lower end, said gas being introduced into the reducing chamber at a plurality of spaced points to minimize the production of eddy currents within the charge in the chamber and thus provide a positive and substantially uniform flow of gas throughout that portion of the chamber directly below the active reducing zone thereof.

6. The improvement in the operation of an upright and continuously operated zinc reducing chamber which comprises maintaining the lower end of the chamber closed against the admission of atmospheric air, and introducing under pressure into the chamber below the active reducing zone thereof an appropriate gas in such volume as to substantially counteract any tendency to a downward flow of zinc Vapor in the lower portion of the chamber, said gas being introduced into the reducing chamber at a plurality of spaced points to minimize the production of eddy currents within the charge in the chamber and thus provide a positive and substantially uniform ,flow of gas throughout that portion of the chamber directly below the active reducing zone thereof.

PHILIP GINDER. ERWIN c. HANDWERK. 

